Lighting units for use in electronic appliances are configured to adopt suitable light sources depending on the characteristics of electronic appliances in order to increase light-emitting efficiency.
Recent lighting units used in electronic appliance may be applied in various ways, for example, to a backlight unit of a flat panel display, an indoor lamp used in an indoor environment, a headlight, a fog light, a backup light, a sidelight, a license plate light, a taillight, a brake light, a turn signal, or a hazard flasher lamp installed on the exterior of a vehicle, or a passenger compartment light installed inside a vehicle.
However, most of these lighting units have adopted a member for increasing the efficiency of transmission of light, such as a light guide plate, in the interest of maximizing the luminance of a surface light source.
In particular, lighting units for vehicles have recently been developed to adopt, as a light source, light-emitting diodes (LEDs), which realize high light-emitting efficiency. In the case of lighting units for vehicles using a surface light source, the use of an LED package as a light source is on the rise. However, when such a LED package is used as a light source, an increase in the number of light-emitting elements constituting a light-emitting surface is necessary in order to achieve a great quantity of light or to realize surface light-emission. The use of a great number of LED packages is problematic in terms of cost and heat radiation as well as in the realization of a circuit between elements due to, for example, curved places or narrow spaces in vehicles, which cause serious disadvantages of high cost and low efficiency. In addition, in the case of a taillight or a location on the vehicle from which light is emitted and which has a curved surface, it is difficult to realize uniform intensity of light over such a light-emitting surface, leading to dark spaces before and after a curved portion. When additional light-emitting elements are used to overcome this problem, an increase in costs is necessarily incurred.